﻿/*
 *
 * (c) Copyright Ascensio System Limited 2010-2020
 *
 * This program is freeware. You can redistribute it and/or modify it under the terms of the GNU 
 * General Public License (GPL) version 3 as published by the Free Software Foundation (https://www.gnu.org/copyleft/gpl.html). 
 * In accordance with Section 7(a) of the GNU GPL its Section 15 shall be amended to the effect that 
 * Ascensio System SIA expressly excludes the warranty of non-infringement of any third-party rights.
 *
 * THIS PROGRAM IS DISTRIBUTED WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE. For more details, see GNU GPL at https://www.gnu.org/copyleft/gpl.html
 *
 * You can contact Ascensio System SIA by email at sales@onlyoffice.com
 *
 * The interactive user interfaces in modified source and object code versions of ONLYOFFICE must display 
 * Appropriate Legal Notices, as required under Section 5 of the GNU GPL version 3.
 *
 * Pursuant to Section 7 § 3(b) of the GNU GPL you must retain the original ONLYOFFICE logo which contains 
 * relevant author attributions when distributing the software. If the display of the logo in its graphic 
 * form is not reasonably feasible for technical reasons, you must include the words "Powered by ONLYOFFICE" 
 * in every copy of the program you distribute. 
 * Pursuant to Section 7 § 3(e) we decline to grant you any rights under trademark law for use of our trademarks.
 *
*/


using System;
using System.IO;
using System.Security.Cryptography;

namespace ASC.Data.Encryption
{
    internal sealed class StreamWrapper : Stream
    {
        private readonly Stream stream;
        private readonly CryptoStream cryptoStream;
        private readonly SymmetricAlgorithm symmetricAlgorithm;
        private readonly ICryptoTransform cryptoTransform;
        private readonly long fileSize;
        private readonly long metadataLength;

        public StreamWrapper(Stream fileStream, Metadata metadata)
        {
            stream = fileStream;
            symmetricAlgorithm = metadata.GetCryptographyAlgorithm();
            cryptoTransform = symmetricAlgorithm.CreateDecryptor();
            cryptoStream = new CryptoStreamWrapper(stream, cryptoTransform, CryptoStreamMode.Read);
            fileSize = metadata.GetFileSize();
            metadataLength = metadata.GetMetadataLength();
        }

        public override bool CanRead
        {
            get { return stream.CanRead; }
        }

        public override bool CanSeek
        {
            get { return false; }
        }

        public override bool CanWrite
        {
            get { return false; }
        }

        public override long Length
        {
            get { return fileSize; }
        }

        public override long Position
        {
            get
            {
                return stream.Position - metadataLength;
            }
            set
            {
                if (value < 0 || value > fileSize)
                    throw new ArgumentOutOfRangeException();

                stream.Position = value + metadataLength;
            }
        }

        public override void Flush()
        {
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return cryptoStream.Read(buffer, offset, count);
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotSupportedException();
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException();
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            throw new NotSupportedException();
        }

        public override void Close()
        {
            cryptoStream.Dispose();
            stream.Dispose();
            symmetricAlgorithm.Dispose();
            cryptoTransform.Dispose();
        }
    }
}
